1. Field of the Invention
The invention concerns a process apparatus for cooling an elongated extruded plastic object while advancing the object in a longitudinal direction through an interior of a closed housing.
2. Description of the Prior Art
Processes for cooling and calibrating elongated, especially continuously extruded plastic objects are already known according to U.S. Pat. No. 5,008,051 or EP-D1-0 487 778 in which the extruded objects or sections are cooled by passage through a continuous cooling chamber. In such a continuous cooling chamber, the extruded section is sprayed on all sides with coolant, especially cooling fluid such as water, usually by means of spraying nozzles, so that by the end of the passage it exhibits an adequate rigidity and in the interior of the continuous cooling chamber a uniform partial vacuum is built up so that on growing cold any collapse of the section walls is prevented. Because of the surface tension of the water, the water or other cooling fluid adheres during spraying to the surface of the section to be cooled so that the subsequently sprayed water or cooling fluid runs off over the existing film of cooling water and thus not all of the sprayed quantity of coolant comes into contact with the surface of the section to be cooled and, therefore, very large quantities of water per unit of time have to be sprayed on to the section in order to achieve a minimal cooling of the section during passage through the continuous cooling chamber.
The underlying task of the present invention is to create a process for cooling and a cooling and calibrating device for extruded objects in which the energy consumption for the cooling of the object can be kept small.
This task of the invention is solved by a process which comprises the steps of dividing the housing interior by support diaphragms into a plurality of consecutive regions including an inlet region at one end of the housing and an outlet region at an opposite end of the housing, passing the object into the inlet region and through calibrating apertures in the support diaphragms into the consecutive regions, and discharging the object from the outlet region, dividing the consecutive regions by a web extending in the longitudinal direction into chambers arranged at respective lateral sides of the object, the web extending a minimal distance from an end face of the object, circulating a cooling liquid though the consecutive regions by delivering the liquid to the inlet region through an inlet port in the housing and removing the liquid from the outlet region through an outlet port in the housing, each chamber at one side of the object being in communication with the chamber at the other side of the object in the consecutive region whereby the circulating cooling liquid flows from the chambers on the one side over the object into the chambers at the other side, and exposing the advancing object to a gradually increasing vacuum in the consecutive regions. In so doing it is advantageous that the vacuum needed to maintain the required quality of the object can be used simultaneously for the transport or for the improved wetting and for the intensified rinsing around the surface of the object. As a result the energy consumption for cooling the objects can be considerably reduced as on account of the better rinsing around the object a higher proportion of the quantity of water delivered comes into direct contact with the surface of the object to be cooled and thus the quantity of heat to be extracted can be extracted with a lower total amount of water per unit of time or with respect to the running meter of a manufactured object.
Furthermore at the same time it is achieved in a surprising manner that the additional consumption of energy to overcome the resistances in the spraying nozzle arrangements, as used in the hitherto known processes and device, is avoided. Linked with this is also the advantage that less primary coolant, especially fresh water, is required as the quantity of coolant turned over and hence the amount lost arising from its turnover is less.
By separating the consecutive regions in a fluid-tight and gas-tight manner, it is possible to use several cooling and/or calibrating devices arranged independently of each other one behind the other or alternatively to use the section contour, which is required anyway for guiding and for stabilising the cross-sectional shape of the objects, simultaneously for subdividing the cooling chamber or the continuous cooling chamber.
The higher vacuum which can act on the object or window section during progressive cooling ensures the dimensional stability and the surface planarity can be used simultaneously for the continuous transport of the coolant over longer longitudinal regions of the object.
Applying gradually increasing vacuum independently to each one of the consecutive regions makes it possible to adjust very delicately and to determine independently in the individual regions the height of the coolant level or of the water level together with the quantity of the overflowing coolant passing around the object.
A simpler process operation is achieved if vacuum pressure is applied to the inlet region and the vacuum is permitted to be gradually increased in the consecutive regions by providing flow openings between the regions, as a result of which the pressure conditions during cooling can be easily kept constant also while the process is being carried out.
A backwash of the coolant can further be prevented if the cooling liquid is drawn from the chamber at one side of the object into the chamber at the other side of the object in the consecutive region by the higher vacuum in the consecutive region and is raised above the object as it flows one side to the other side.
A favourable throughflow and agitation of the coolant and a simple control of the quantity of coolant to be passed through the region in unit time is achieved by jointly exhausting the vacuum and removing the cooling liquid from the outlet region.
The task of the invention is, however, also solved independently of the solution according to the process, by the cooling and calibrating apparatus for cooling an elongated extruded plastic object while advancing the object in a longitudinal direction, which comprises a closed housing comprising a cover plate, a bottom plate, two end walls and two side walls, the cover plate, bottom plate and walls defining an interior wherethrough the object is advanced in the longitudinal direction from an inlet region at one end wall of the housing to an outlet region at an opposite end wall, consecutive support diaphragms dividing the interior into consecutive regions, the support diaphragms having calibrating apertures through which the object passes and is advanced, a web extending in the longitudinal direction and dividing the consecutive regions into chambers arranged at respective lateral sides of the object, the web extending a minimal distance from an end face of the object, an inlet port in the housing for delivering a circulating cooling liquid to the inlet region and an outlet port in the housing for removing the liquid from the outlet region, each chamber at one side of the object being in communication with the chamber at the other side of the object in the consecutive region whereby the circulating cooling liquid flows from the chambers on the one side over the object into the chambers at the other side, and means for applying a gradually increasing vacuum to the consecutive regions. The means for applying a gradually increasing vacuum comprises an exhaust port in the outlet region of the housing, a vacuum pump having an intake connected to the exhaust port, and an intake port in the inlet region of the housing, the intake port being connected to an output of the vacuum pump. It is advantageous with such a solution that only by arranging an additional longitudinal web for subdividing the continuous cooling chamber into different longitudinal regions can the vacuum arranged in the cooling chamber or its housing be used for the transport of the coolant through this housing.
A further independent construction of the cooling and calibrating device with which the task of the invention can likewise be solved an embodiment wherein the web extends from the cover plate towards the end face of the object. Partitions are mounted on the consecutive support diaphragms, the partitions being alternately arranged between the cover plate, the web and one of the side walls and the other one of the side walls whereby the chambers in the consecutive regions at each side are closed off from each other. The advantage of this solution lies in that the longitudinal regions of an object or of a section lying opposite each other are ever more strongly cooled in successive regions and somewhat less strongly in a region immediately connected to that so that the strains building up during the more rapid cooling can be balanced out again in the subsequent region in which a smaller reduction of the temperature of the object or a smaller removal of heat takes place.
In a further embodiment, the web extends from the bottom plate towards the end face of the object, and channels below the bottom plate connect the inlet and outlet ports for the cooling liquid. This is advantageous as by the dimensioning of the channels the rate of flow or the intermixing of the coolant can be reinforced so that parts of the coolant at a higher temperature can be cooled down again to a lower average temperature by the additional quantity of coolant as a result of which the cooling effect of the entire cooling and calibrating device can be additionally increased.
If the inlet and outlet ports are arranged in the support diaphragms, it is possible to make do with a lower volume for the coolant and less technical outlay for the manufacture of the cooling and calibrating device and it is also simple to achieve the adjustment of the different partial vacuums in the individual regions when the cooling and calibrating device is started up.
According to another embodiment, flow conditions or turbulence remain approximately constant but are also improved in the first and last region in the direction of extrusion with an apparatus further comprising a tank holding the cooling liquid, a pump having an intake connected to the tank and an output, a pipe connecting the pump output to the inlet port in the housing for delivering the cooling liquid to the inlet region, and a pipe connecting the outlet port in the housing to the tank for removing the liquid from the outlet region into the tank.
It is also advantageous, if the apparatus further comprises a vacuum pump, a cyclone following the vacuum pump and another pump for the cooling liquid arranged in the connecting pipe between the outlet port and the tank, that means in energy efficiency terms a more favourable exhaustion of the air, for producing the vacuum, and of the coolant required for cooling is achieved.
It is of advantage if the one end wall has an intake opening receiving ambient air so that generally throughout the cooling and calibrating device and throughout the respective region a simpler formation of the vacuum can occur.
If the support diaphragms have flow openings permitting the air to pass therethrough, the entire cooling and calibrating device can be evacuated in a simple manner with a single pump. Also, an exhaust pipe may lead to a single vacuum pump used to establish gradually increasing vacuum pressures in the consecutive regions.
If the means for applying the gradually increasing vacuum comprises a vacuum pump and a separate pipe connecting each region to the vacuum pump, a sensitive and independent regulation of the vacuum in the individual regions can be achieved with which the differences in the partial vacuum in the individual immediately adjacent regions can be determined more freely.
The gradually increasing vacuum causes the level of the cooling liquid in each chamber at one side of the object to be higher than in the chamber at the other side of the object in the consecutive region so that a height difference is produced between the water columns in the two chambers following immediately on each other which achieves a gushing overflow and hence a good and strongly changing wetting of the section and thus a considerable cooling effect.
It proves advantageous to increase the vacuum gradually by at least 0.002 bar, preferably 0.005 bar, as by that means a difference in level between the water levels located in the two chambers following immediately on each other in a region can be so determined that the upper side of the section and a part of the upper lateral edge is intensively cooled when the coolant overflows.
If the minimal distance of the web from the end face of the object is between 0.5 mm and 5 mm, even in those regions in which the longitudinal web is facing the object or the window section, a good flow of coolant and hence also a good cooling effect adapted to the other regions is achieved.
If the support diaphragms are spaced from each other in the longitudinal direction from the inlet to the outlet region at increasing distances, in accord with the continuous hardening of the object during passage through the cooling and calibrating device on account of the cooling, those segments over which an intensive cooling occurs become larger and larger and furthermore with a lower number of regions a higher cooling effect can be achieved.
The side walls of the housing may have recesses displaceably receiving and holding the support diaphragms, and the recesses may have end faces defining a distance extending perpendicularly to the longitudinal direction and exceeding the width of the support diaphragms. In this way, the section contour contained in the support diaphragms can simply adapt to tolerance fluctuations or oscillations in the object or window section passing through as a result of which impairments in the surface of the object are adequately avoided.
If the support diaphragms have ports close to the calibrating apertures, continuous laminar flows can be set up over the entire length of the cooling and calibrating device which make possible an intensive cooling of the surface regions over the different longitudinal regions of the object.
The bottom plate may define flow channels recessed into the bottom plate and facing the interior of the housing, the flow channels being in communication with the chambers in the consecutive regions, and the flow channels may extend parallel to the longitudinal direction. Also, the flow channels may span the consecutive regions and extend from one of the regions to at least the center of the consecutive region in the longitudinal direction. The flow channels may have a rectangular cross section in plan view as well as in a plan extending perpendicularly to the longitudinal direction. The flow channels may also have a concave cross section in a plan extending perpendicularly to the longitudinal direction, and they may be offset from each other in a direction extending perpendicularly to the longitudinal direction. The flow channels may overlap consecutive ones of the regions. Furthermore, the apparatus may comprise a plurality of the flow channels between consecutive ones of the regions, and respective ones of the flow channels may be alternately arranged in the longitudinal direction between the web and a respective one of the side walls. These features make a plurality of different advantages possible especially in that in the immediate vicinity of the object the coolant is shifted into a higher flow rate and thus the relative velocity between the more rapidly flowing coolant and the object likewise advancing in the extrusion direction can be produced more simply which in turn initiates a higher wetting frequency of the surface of the object by the coolant and thus leads over all to an essentially more efficient cooling of the object with a considerably lower consumption of coolant.
Finally a good and intensified cooling action of the extruded object is also achieved by the following features: the flow channels may have side walls facing side walls of the web facing the side walls of the housing, the side walls of the channels being flush with the side walls of the web or spaced from the side walls of the web by less than 10 mm. The support diaphragms may have rectangular openings having a length extending perpendicularly to the bottom plate which exceeds a width thereof extending parallel to the bottom plate and transversely to the longitudinal direction. Furthermore, the support diaphragms may have openings arranged between the calibrating apertures and the cover plate, the openings having lower edges spaced from upper edges of the calibrating apertures. Also, the support diaphragms may have openings offset from the calibrating apertures in a direction extending perpendicularly to the longitudinal direction. The web may have a thickness of less than 10 mm, preferably less than 5 mm, extending perpendicularly to the longitudinal direction.